Study On The Influence Of Propagation Law Gas Explosion In Underground Utility Tunnel With Porous Structure

The construction of an underground utility tunnel has benefit to the overall development planning of the city’s future municipal pipeline integration.However,the construction of underground utility tunnel began late in China,and it is very dangerous to put gas pipelines inside.Due to the special structure of the pipe gallery,once leakage and explosion occur in the gas tank,chain reaction will be caused and endangers the safety of the overall security of underground network systems.However,there are no explosion protection specifications for pipe racks,and the existing explosion suppression devices have defects.Therefore,it is necessary to study the propagation law of explosion waves in the underground utility tunnel from the viewpoint of the structures blast resistance,and quantifying the suppression effect of porous structures on explosions so as to reduce the impact of explosion accidents caused by gas tanks in the underground utility tunnel,and provide reference for improving the gas tanks explosion resistance design.Taking the actual project of Changsha Yingbin Avenue as the research object,combined with the material characteristics of porous structures,it is proposed to use porous structure to change boundary conditions to reduce explosion damage.This thesis used Computational Fluid Dynamics(CFD)as the analysis method and takes the methane air premixed gas in the underground comprehensive pipeline gallery gas tank as the research object.A model is established by using 3D design software,and ICEM is used to divide the grid.Combined with the simulation platform of Flunet20.0,a physical model of component transportation was used to define the gas state,the resistance source term of the flow equation was added in the governing equations,and the parameters and properties of the porous structure were set,Using the Realizable k-epsilon turbulence model and velocity pressure coupled PISO algorithm,the explosion process in the gas tank of the pipeline gallery was simulated under different built-in porous structure porosity,unit length,and relative position parameters of the ignition source,and the influence of four parameters on the propagation of explosion in the underground comprehensive pipeline gallery gas tank was analyzed.The obtained results are as follows:1.The interference of porous structure to explosion propagation is obvious.Under the influence of porous structure,the explosion propagation in a gas tank is influenced by both the parameters of the porous structure and the deflagration characteristics of the premixed gas.Because the tiny pores within the porous structure can absorb more pressure and combustion waves,so the explosion can’t be sustained and explosion is suppressed.At the same time,when the flame passes through the porous structure,the small pores inside the porous structure will induce the flame turbulent,so as to promote the propagation of the explosion.Therefore,there is an obvious competition between the two mechanisms in the process of explosion propagation.When the inhibition mechanism of the porous structure exceeds the promotion mechanism and dominates,fire and explosion will be prevented.2.The porous porosity affects the explosive overtemperature and overpressure.Under the working condition without porous structure,the explosion overtemperature reached 3572 K,and the explosion overpressure reached 1.86 MPa.Under the porous structure an obvious temperature buffer zone is formed behind the porous structure.The explosion overtemperature increases firstly and then decreases with the increasing porosity.Under the action of a 60%porosity porous structure,the value of explosion overtemperature is 3444 K,and the overpressure is 1.82 MPa,This effectively inhibits the growth of both explosion overtemperature and overpressure.3.The suppression effect of the explosion flame and the attenuation effect of overpressure increase with the increasing length of porous structure.When the length of a porous structure is 1m,the maximum temperature is much higher than that without porous structure cabin.However,as the length of the porous structure increases to 5m,the cabin overtemperature is basically the same as that without porous structure cabin.So,there exists a certain length between 3m and 5m to make the two mechanisms inside the explosion to be balanced with each other.When the length increases to 8m,the maximum explosion overtemperature can decrease by 122 K.4.relative ignition source position has an impact on the explosion propagation.As the distance between the porous structure and the ignition source increases,the more energy is lost during the explosion propagation process,and less total volume value of energy is absorbed by the porous structure.The porous structure at 20 m can absorb the explosive energy mostly.Combining the two evaluation indicators of explosion overpressure and overtemperature,The evaluation of the ten conditions in this article is based on the comprehensive evaluation of quenching parameters.The comprehensive index of explosion overpressure attenuation and flame temperature suppression has a linear relationship with the porous structure parameter.Placing a porous structure with unit length of 8m with a 60% porosity at an interval of 20 m in an underground utility tunnel can effectively reduce explosion overtemperature,reduce flame temperature up to 10%,overpressure by up to33%,and flame speed by up to 33%.